Project Summary/Abstract Clinical Problem and Significance: Parkinson's disease (PD) affects approximately 1.5 million people in the United States, and nearly 2% of veterans. Each year, 40,000 veterans are treated for PD by the Veterans Health Administration. PD is a chronic neurodegenerative condition characterized by motor dysfunctions such as bradykinesia, rigidity, tremor, postural instability, and gait abnormalities. Among gait abnormalities, freezing of gait (FOG), an episodic inability to generate effective stepping, is reported as one of the most debilitating and distressing symptoms for persons with PD. FOG is a leading cause of falls, which makes it a clinically relevant problem leading to increased morbidity and mortality. The precise neurological mechanism causing FOG is unknown, but impaired gait automaticity may cause individuals to rely more heavily on cortical control for locomotion. Due to the roles of the frontal and parietal regions in attentional processing and visual and somatosensory integration, they are emerging as areas of interest for the compensatory control of gait. This concept is supported by imaging studies showing increased frontal and parietal lobe activity in individuals with PD as a result of frontal/striatal dopaminergic deficits and disrupted basal ganglia control of automaticity. In this proposal, we plan to use a functional imaging technique (functional near-infrared spectroscopy, fNIRS) to examine frontal and parietal cortical involvement contributing to FOG. The Specific Aims of this study are: 1) to characterize the role of frontal and parietal cortex activation during gait task in PD+FOG, PD-FOG, and matched controls using fNIRS; 2) to determine the extent to which a competing cognitive task affects frontal and parietal activation during gait tasks for PD+FOG, PD-FOG, and matched controls using fNIRS; and 3) to determine the test-retest reliability of fNIRS for gait tasks in individuals with PD+FOG, PD-FOG and matched controls. All participants will be evaluated while completing three tasks: 1) walking overground; 2) walking while performing a cognitive task; and 3) performing the cognitive task in isolation. This pilot project will generate data on the magnitude of motor- and cognitive-related fNIRS activation patterns in participants with PD, as well as the test-retest reliability of these measures. Understanding of the neural mechanisms involved in freezing of movement will assist in the development of potential new strategies and therapies for improving ambulation for individuals with PD.